1. Field of the Invention
This invention relates generally to the field of multimedia systems. More particularly, the invention relates to a multimedia system capable of intelligently processing and storing several independent broadcast multimedia streams (e.g., broadcast cable or satellite streams).
2. Description of the Related Art
A prior art system for receiving broadcast multimedia signals is illustrated in FIG. 1. The system includes one or more tuners 120, 121 configured to lock on to multimedia signals 100, 101 transmitted at a carrier frequency and down-convert the signals to baseband signals. Quadrature Amplitude Modulation (“QAM”) demodulators 130, 131 demodulate the baseband signals to extract the underlying digital content. As is known in the art, QAM is a modulation technique employed by cable and satellite providers that generates four bits out of one baud. For example, a 600 baud line (600 shifts in the signal per second) can effectively transmit 2,400 bps using this method. Both phase and amplitude are shaped with each baud, resulting in four possible patterns. As indicated in FIG. 1, certain multimedia systems (primarily satellite systems) use a different modulation technique known as Differential Phase Shift Keying (“DPSK”) rather than QAM to demodulate the multimedia signals 100–101.
The video signal demodulated by the QAM/DPSK demodulators 130, 131 contains a plurality of statistically multiplexed multimedia streams, each containing content for a single cable or satellite “channel” (e.g., HBO). Satellite systems employ a series of transponders for receiving the multiplexed streams and cable systems typically receive the multiplexed streams over 6 Mhz channels. In either case, the multiplexed streams are transmitted at a combined data rate of approximately 40 Mbits/second, as indicated in FIG. 1.
Referring to FIG. 2, each stream/channel may be identified by a predetermined group of packet identification (“PID”) codes. PID filter modules 140, 141 extract all packets from the set of multiplexed streams having PID codes associated with a specified stream (e.g., the stream which a user is currently watching). For example, in FIG. 2, PID 7 identifies the specified stream's video content and PIDs 5 and 6 identify the stream's audio left and audio right, respectively. Various additional PIDs may be associated with a stream and used to transmit channel-specific data/content (e.g., dolby digital content, . . . etc).
The multimedia content contained in the stream is then stored on a mass storage device 160, which may be used for temporary storage and/or long term storage of the content. Temporary storage features include pause and rewind functions for live television broadcasts and the ability to begin watching a program after the designated start time for the program. Long term storage functions include the ability to record entire programs for later viewing (similar to the functions provided by standard VCR). The multimedia content is then decompressed/decoded by one or more MPEG-2 decoder modules 170 before being rendered on a television display 135.
As illustrated in FIG. 1, prior art systems may also utilize a main memory 126 for storing instructions and data and a central processing unit (“CPU”) 125 for executing the instructions and data. For example, the CPU may provide a graphical user interface displayed on the television, allowing the user to select certain television or audio programs for playback and/or storage on the mass storage device 120. In addition, prior art system also include one or more conditional access modules (not shown) for preventing users from viewing programs which they do not have the right to view (e.g., subscription-based channels such as HBO and pay-per-view events).